The invention relates to a method for metering fuel from a high pressure system, comprising at least one high pressure pump, one pressure accumulator and one high pressure injection valve, into an exhaust gas duct of an internal combustion engine in order to regenerate a nitrogen oxide storage catalytic converter disposed in the exhaust gas duct, wherein a high pressure of the fuel is generated by the electrically actuated high pressure pump, which discretely delivers the fuel and has a constant stroke volume, wherein the fuel is supplied to the pressure accumulator comprising a pressure measuring device for determining the fuel pressure and wherein the fuel is injected into the exhaust gas duct via the downstream, electrically actuated high pressure injection valve.
The invention relates further to a method for metering fuel from a high pressure system, comprising at least one high pressure pump, one pressure accumulator and one high pressure injection valve, into an exhaust gas duct of an internal combustion engine in order to regenerate a particle filter disposed in the exhaust gas duct, wherein a higher pressure of the fuel is generated by the electrically actuated high pressure pump, which directly delivers the fuel and has a constant stroke volume, wherein the fuel is supplied to the pressure accumulator comprising a pressure measuring device for determining the fuel pressure and wherein the fuel is injected into the exhaust gas duct via the downstream, electrically actuated high pressure injection valve.
The invention further relates to a control unit for carrying out the method.
In order to reduce toxic emissions of internal combustion engines, different catalysts and filters are provided today in exhaust gas aftertreatment systems that are correspondingly provided. Thus, for example, in the case of diesel engines, diesel particle filters and NOx storage catalysts can be provided in addition to oxidation catalysts for oxidizing hydrocarbons and carbon monoxide.
Particle filters are used for reducing particle emissions. The exhaust gas is led through the particle filter, which separates out solid particles and retains said particles in a filter substrate. As a result of the soot masses embedded in the filter substrate, the particle filter becomes clogged with time. This fact is detected by an increase in the flow resistance and thereby in the exhaust gas back pressure. For this reason, the embedded soot mass must be discharged from time to time in a regeneration process. The regeneration is introduced by an increase in the exhaust gas temperature to typically 600° C. to 650° C., so that the soot embedded in the particle filter begins to burn off. In particular at low loads on the internal combustion engine and low rotational speeds of said internal combustion engine, measures inside the engine itself are to be provided in order to achieve the necessary temperatures for regeneration, for example in the fuel-mixture generation of the engine or by measures taken downstream of the engine such as an afterinjection (HCI: hydrocarbon injection) into the exhaust gas duct, which combusts at the oxidation catalyst. When the exhaust gas temperature is sufficiently high, an exothermal reaction is initiated in the particle filter, which causes a burn-off of the soot particles and regenerates said particle filter within a matter of minutes (e.g. 20 minutes).
NOx storage catalysts (NSC: NOx storage catalyst) serve to reduce the NOx emissions from internal combustion engines. During the operation of the internal combustion engine, NO2 is embedded in the NOx storage catalyst. NO is thereby oxidized to NO2 in an upstream oxidation catalyst. If the NO2 storage limit of the NOx storage catalyst is achieved, said NOx storage catalyst must be regenerated. In order to provide the carbon monoxide necessary for this purpose, the exhaust gas must have a lambda value >1. In the case of lean running diesel engines, provision can also be made for the injection of fuel into the exhaust gas duct.
The German patent specification DE 10 2008 013 406 A1 describes a device for metering at least one emission reducing medium into an exhaust gas system, in particular for introducing fuel into an exhaust gas tract in order to regenerate an emission reducing element in the exhaust gas tract, comprising at least one injection valve, in particular a pressure-controlled injection valve, and at least one feed line for feeding the emission reducing medium to the injection valve, wherein at least one pressure damper is provided in the feed line upstream of the injection valve. In such a system, fuel from a low pressure system, which is supplied by a continuously operating low pressure pump, is, for example, metered via a metering valve and injected into the exhaust gas duct via the pressure-controlled injection valve.
Based on such a device, the German patent specification DE 10 2004 056 412 A1 describes a method for operating an internal combustion engine, in the exhaust gas region of which an exhaust gas treatment device is disposed, in which method a reagent is introduced into the exhaust gas region upstream of the exhaust gas treatment device, in which method initially an adjustable reagent safety valve (ReaCV), then a continuous reagent metering valve (ReaDV) and thereafter a reagent introduction check valve (ReaIV) are disposed in the direction of flow of the reagent, which is brought to a predefined reagent source pressure (pQRea), in which method the reagent pressure (pRea) is detected in the reagent path, which lies between the reagent metering valve (ReaDV) and the reagent introduction check valve (ReaIV), in which method the reagent pressure (pRea) detected in at least one predefined state of the reagent safety valve (ReaCV) and/or the reagent metering valve (ReaDV) is compared to at least one threshold value (pU, pabg, dpReaIV, pQRea, dpRea/dt) and a fault signal is outputted if the threshold value is exceeded. The method facilitates a check as to whether a leak is present in the reagent path and a check of the function of the valves provided therefore.
Aside from the low pressure injection systems described, metering systems are known, which introduce reagent into the exhaust gas duct at high pressures. Such systems are configured from a low pressure system and a high pressure system and facilitate, for example, the introduction of fuel into the exhaust gas duct. The low pressure system delivers the fuel from a tank to a high pressure pump of the high pressure system. The high pressure pump relates, for example, to a magnetically operated pump, which discretely delivers the fuel and has a constant stroke volume, which pump compresses the fuel to a high pressure, for example to 30 bar. The fuel is sprayed into the exhaust gas duct via a downstream high pressure accumulator, which can be embodied as a piston accumulator, and a high pressure injection valve (HDEV).